Nondestructive Inspection (NDI) determines the quality of a workpiece without causing damage to the workpiece. One NDI technique uses acoustic waves to inspect a work-piece. This technique directs an incident acoustic wave at a workpiece, senses a reflection from the workpiece and analyzes the reflection to determine the quality of the workpiece. Acoustic inspection is helpful, for example, to determine the integrity of airplane components including the wing, fuselage and empennage by detecting disbonded lap splices, corroded rivet joints and similar structural defects.
A typical apparatus for acoustically inspecting a workpiece includes a pulse generator electrically connected to a transducer assembly which generates a focused acoustic wave (practical ultrasonic transducers have an inherent focus and the selection of a useful focus is application dependant). The acoustic wave travels through a transmission medium and onto the workpiece. Acoustic reflections from the workpiece radiate back to the transducer and causes the transducer to generate a corresponding electrical signal. A processor then analyzes the electrical signal to determine the quality of the workpiece.
Ultrasonic NDI, in particular can improve the inspection spatial resolution and the signal to noise by using a focused acoustic beam and a scanner to move the transducer assembly in a raster scan over the workpiece. This type of NDI requires good and reliable acoustic coupling and is most effective when applied in an immersion mode.
A known inspection apparatus as described by Patton in the U.S. Pat. No. 5,469,744 uses an acoustic apparatus called a Contact Adaptive Bubbler (CAB) consisting of a tubular member containing an ultrasonic transducer and a couplant chamber (first chamber) and a couplant reservoir (second chamber) between the transducer and the workpiece. Couplant is continuously supplied to replenish couplant leaks. A vacuum chamber (opening) recovers couplant that leaks from the couplant reservoir (second chamber).
However, in practice, it was found that the prior art inspection device operates reliably on horizontal and slightly angled workpiece surfaces, but not on rough surfaces, and in vertical and underside orientations (inverted) with respect to workpiece surfaces. Further, the couplant and vacuum lines connected to prior art devices easily disturbs the horizontal and slightly angled orientations of those device with respect to the workpiece, thus minimizing the reliability of the prior art devices even in those orientations. Additionally, the prior art devices cannot reliably be used on rough surfaces, or vertical or under side surfaces as a result of shortcomings of the interface of those devices to the surface of interest. The acoustic inspection device of the present invention overcome the problems experienced by the prior art thus permitting use on rough surfaces and in any orientation from horizontal to inverted.